Frequent battles have continued since then, amid claims of war crimes by Islamist forces against Kurdish civilians.

An Iraqi official told The Associated Press that the Baghdad government had brought Iraqi reinforcements to its side of the border to prevent the violence spilling over.

He described the fighting as "heavy battles in which all types of weapons were used."

The border crossing was under the Syrian government's control until March, when it was taken by Islamist rebels.

Syria's Kurdish minority makes up around 10% of the population and is largely concentrated in the country's far north-east, near the borders with Turkey and Iraq.

The Kurds are the Middle East's largest nation without a state. Their ancestral homeland, known as "Kurdistan", is currently occupied by four countries - Iran, Iraq, Turkey and Syria - although Kurds in Iraq now enjoy autonomy under the Kurdish Regional Government (KRG).

Syria’s civil war, originally a war between Syrian President Bashar Al-Assad’s regime and rebels trying to oust him, is now essentially three wars. In addition to clashes between Assad’s army and rebels and the clashes between jihadists and Kurds, the more moderate rebel groups and the Islamist extremist groups are also fighting each other.

As the fighting has continued, thousands of Syrian Kurds seeking to escape persecution at the hands of Jihadists, have been crossing the border into the autonomous Kurdish area of northern Iraq.

Meanwhile, Kurdish groups inside Syria are making moves to establish an autonomous Kurdish region, along similar lines to the KRG in Iraq.